summer/ winter pots replace soil or not?

Hello, 

I have a couple of large tubs that I replace the soil each time I replant, whether it's planting up a winter pot or summer pot. I tip the spent soil onto my borders.

But I was wondering if I could not replace the soil for a few seasons and just improve its nutrients by adding some chicken pellets, or something.

Obviously, after a few seasons, I would replace.

Thanks for reading.